The present invention relates to a control system for what is termed as a twin-clutch transmission. The twin-clutch transmission is configured to set up multiple transmission gear stages by use of a first power transmission path for transmitting a driving force of an engine to driving wheels via a first clutch, and to set up the other multiple transmission gear stages by use of a second power transmission path for transmitting the driving force of the engine to the driving wheels via a second clutch.
Such a twin-clutch transmission is designed to accomplish shift-up and shift-down by repeatedly sequentially carrying out: the pre-shifting of an even-numbered speed transmission gear stage while an odd-numbered speed transmission gear stage is being set up with engagement of the first clutch; the setting up of the even-numbered speed transmission gear stage once the second clutch is engaged in exchange for disengagement of the first clutch; the pre-shifting of an odd-numbered speed transmission gear stage while the even-numbered speed transmission gear stage is being set up with the engagement of the second clutch; and the setting up of the odd-numbered speed transmission gear stage once the first clutch is engaged in exchange for disengagement of the second clutch.
Japanese Patent Application Laid-open No. 2008-309217 has made publicly known a transmission control system which achieves reduction in the number of shift valves by making shift valves commonly used both as shift valves for selectively supplying a hydraulic pressure to the first or second clutch, and as shift valves for selectively supplying a hydraulic pressure to a first or a second hydraulic actuator.
Meanwhile, even in a case where one of the shift valves each configured to distribute a hydraulic pressure to engagement means for setting up transmission gear stages goes out of order in such a twin-clutch transmission, a vehicle can run to a car service shop if either a first predetermined transmission gear stage in the first power transmission path or a second predetermined transmission gear stage in the second power transmission path is designed to be capable of being set up. This enhances convenience in emergency situations. In this case, if dedicated redundancy means are installed in the twin-clutch transmission for the purpose of counteracting the anticipated possible failure in the shift valves, such installation causes increase in costs and weight. For this reason, it is desirable that only minimum necessary measures using the existing hydraulic circuit should be taken to enable the vehicle to run when one of the shift valves goes out of order.